Preferential transposition of aDrosophila P element to the corresponding region of the homologous chromosome

Genetic and physical analyses have demonstrated an intimate interaction or pairing of homologous chromosomes in the nuclei of manyDrosophila cell types. Experiments were performed to determine whether P elements transposing from a given chromosome to its homolog would preferentially insert in the region corresponding to the donor site, perhaps due to such a proximity. AP[lacZ;ry ⁺] element at thecactus locus (35F) on the second chromosome was mobilized and 96 insertions on the homolog were recovered. The distribution of these new insertions was determined by recombination mapping and molecular analysis, and compared with a control set of 93 second-chromosome insertions originating from theX chromosome. A nearly threefold preference was observed for re-insertion in a region of two to three number divisions aroundcactus on the homolog. However, none of these local insertions was actually within 50 kb of the site atcactus corresponding to the starting site. This is in marked contrast to the previously described phenomenon of intrachromosomal local transposition, where the majority of local transpositions are within 10 kb. The data suggest that the mechanisms for intrachromosomal and interchromosomal local transposition are distinct, and are consistent with a model for interchromosomal local transposition involving proximity of homologous chromosomal regions in the nuclei of the germline cells.     

Two distinct P element subfamilies in the genome of Drosophila bifasciata

The genome of Drosophila bifasciata harbours two distinct subfamilies of P-homologous sequences, designated M-type and O-type elements based on similarities to P element sequences from other species. Both subfamilies have some general features in common: they are of similar length (M-type: 2935 bp, O-type: 2986 bp), are flanked by direct repeats of 8 by (the presumptive target sequence), contain terminal inverted repeats, and have a coding region consisting of four exons. The splice sites are at homologous positions and the exons have the coding capacity for proteins of 753 amino acids (M-type) and 757 amino acids (O-type). It seems likely that both types of element represent functional transposons. The nucleotide divergence of the two P element subfamilies is high (31%). The main structural difference is observed in the terminal inverted repeats. Whereas the termini of M-type elements consist of 31 by inverted repeats, the inverted repeats of the O-type elements are interrupted by non-complementary stretches of DNA, 12 by at the 5 end and 14 by at the 3 end. This peculiarity is shared by all members of the O-type subfamily. Comparison with other P element sequences indicates incongruities between the phylogenies of the species and the P transposons. M-type and O-type elements apparently have no common origin in the D. bifasciata lineage. The M-type sequence seems to be most closely related to the P element from Scaptomyza pallida and thus could be considered as a more recent invader of the D. bifasciata gene pool. The origin of the O-type elements cannot be unequivocally deduced from the present data. The sequence comparison also provides new insights into conserved domains with possible implications for the function of P transposons.     

A new approach for rhizosphere research by X-ray microanalysis of microliter soil solutions

Lolium perenne growing with high root density on a fine nylon mesh (Kuchenbuch and Jungk, 1982) caused the development of element gradients in the rhizosphere below the mesh. Micro-liter soil solutions from 2-mg soil samples were sprayed onto Formvar-coated grids and analyzed by X-ray microanalysis in a transmission electron microscope. The results were comparable to those obtained by flame photometry and atomic absorption spectrometry (AAS) of conventional soil solutions from 1 g soil. X-ray microanalysis of micro-soil solutions allows the application of different extraction procedures to even small amounts of soil usually available from rhizosphere experiments. Information about soil buffering characteristics in the rhizosphere can thus be obtained. Aluminum accumulation in the rhizosphere of small segments of single Picea abies fine roots grown in undisturbed natural forest soil could be detected with this technique.     

Microelectrode-recorded development of the symplasmic autonomy of the sieve element/companion cell complex in the stem phloem of Lupinus luteus L.

From the cambial stage onwards, the symplasmic autonomy of sieve element/companion cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intracellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multicellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.Abbreviations LYCH Lucifer Yellow CH - membrane potential - PMF proton-motive force - PP phloem parenchyma cell - SE/CC-complex sieve element/companion cell complex - SR-G sulphorhodamine G     

广西崇左县冲塘新石器时代人骨微量元素的初步研究

本文对广西崇左县冲塘新石器时代的３个个体（Ｍ０２,Ｓ０８,Ｓ０９）的肢骨进行了化学元素（Ｓｒ,Ｚｎ,Ｃａ,Ｐ,Ｃｄ,Ｐｈ）的含量测定．并根据研究结果对当时人类的生活环境、食物性质作了推测和分析．     

田林老山中山两类森林凋落物研究

田林老山中山两类森林凋落物研究梁宏温（广西农学院林学分院,南宁５３０００１）ＳｔｕｄｉｅｓｏｎｔｈｅＬｉｔｔｅｒｆａｌｌｏｆＴｗｏＦｏｒｅｓｔＴｙｐｃｓｉｎＭｉｄ—ＡｌｔｉｔｕｄｅｏｆＬａｏｓｈａｎＭｏｕｎｔａｉｎｉｎＴｉａｎｌｉｎＣｏｕｎｔｙ．￥Ｌ...     

结球甘蓝离体下胚轴愈伤组织的维管组织及管状分子

结球甘蓝离体下胚轴培养初期,在切口较深层发现的维管组织结节,是由外植体维管组织衍化的。愈伤维管组织既可由愈伤薄壁细胞分化,也可由愈伤形成层分化。愈伤形成层向内分化导管分子,向外没有发现筛分子的分化。愈伤维管组织有不同的形态,起初常各不相连,后和外植体维管组织衔接。芽的再生起初和愈伤维管组织没有直接的联系,后原形成层自上而下分化,逐渐与愈伤维管组织相连接。不定根发生于维管组织结节的单向极性分化,始终     

Similar tissue-specific expression of the Adh genes from different Drosophila species is mediated by distinct arrangements of cis-acting sequences

In Drosophila melanogaster transformants, the alcohol dehydrogenase (Adh) genes from D. affinidisjuncta and D. grimshawi show similar levels of expression except in the adult midgut where the D. affinidisjuncta gene is expressed about 10- to 20-fold more strongly. To study the arrangement of cis-acting sequences responsible for this regulatory difference, homologous restriction sites were used to create a series of chimeric genes that switched fragments from the 5 and 3 flanking regions of these two genes. Chimeric genes were introduced into the germ-line of D. melanogaster, and Adh gene expression was analyzed by measuring RNA levels. Various gene fragments in the promoter region and elsewhere influence expression in the adult midgut and in whole larvae and adults. Comparison of these results with earlier studies involving chimeras between the D. affinidisjuncta and D. hawaiiensis genes indicates that expression in the adult midgut is influenced by multiple regulatory sequences and that distinct arrangements of regulatory sequences can result in similar levels of expression both in the adult midgut and in the whole organism.